Slurry compositions for ground improvement using blast-furnace slag cement and method of producing soil cement slurry by using same

ABSTRACT

Slurry composition for ground improvement is obtained from cement, water and an admixture. The slurry composition cement is of a kind prepared by using blast-furnace slag cement of a specified type as the cement at a water/blast-furnace slag cement mass ratio of 40-250% and contains the admixture in an amount of 0.1-5 mass parts for 100 mass parts of the blast-furnace slag cement. The blast-furnace slag cement of the specified type contains blast-furnace slag fine particles with fineness 3000-13000 cm 2 /g in an amount of 60-80 mass % and portland cement in an amount of 20-40 mass % for a total of 100 mass %.

This application is a continuation of International Application No.PCT/JP2010/059699, filed Jun. 8, 2010, priority being claimed onJapanese Patent Application 2009-138002 filed Jun. 9, 2009.

BACKGROUND OF THE INVENTION

This invention relates to slurry compositions for ground improvementusing blast-furnace slag cement and a method of producing soil cementslurry by using such slurry compositions.

In recent years, the demand for reducing the emission rate of carbondioxide and improving efficient energy consumption is becomingincreasingly stronger. Under this condition, blast-furnace slag asby-product from steel mills is being effectively used as material forblast-furnace slag cement in the form of blast-furnace slag fineparticles in mountain stationary construction, underground water stopconstruction and soft ground improvement construction works. Generally,when such a ground improvement work is carried out, cement slurry with amixture of cementatious stabilizer and water (cement milk) is injectedinto the ground and a drilling and kneading machine is used to mix andstir it with the ground at the site, and blast-furnace slag cement isused here as the cementatious stabilizer. Blast-furnace slag cement isusually produced by mixing blast-furnace slag fine particles into normalportland cement and is usually divided according to the JIS-RS211standard into the following three kinds, depending on the amount of theblast-furnace slag fine particles: Type A (over 5% to 30%), Type B (over30% to 60%) and Type C (over 60% to 70%). Type B with a good balance incharacteristics is usually used when actual ground improvement is done.

For ground improvement, Type B blast-furnace slag cement is normallymixed into 1 m³ of ground at a rate of 100-400 kg, but since about 400kg of carbon dioxide is emitted for producing 1 ton of Type Bblast-furnace slag cement, this means that 40-160 kg of carbon dioxideis emitted for improving 1 m³of ground by using Type B blast-furnaceslag cement, exclusive of the emission of carbon dioxide generated bythe operation of construction machines, transportation of materials,etc. For this reason, in the field of carrying out ground improvement,there have been demands for the development of technology forsuppressing the generation of carbon dioxide by using blast-furnace slagcement at a higher rate, while maintaining workability and theprerequisite that the ground to be improved gain the necessary strength.

The present invention relates to slurry compositions for groundimprovement using blast-furnace slag cement that can respond to suchdemands, as well as a method of producing soil cement slurry using suchcompositions.

Regarding the effects of the conventional use of portland cement forground improvement, it has been reported, for example, in “Manual forGround Improvement by Cementatious Stabilizer” (1984) pages 42-44,edited by the Cement Association of Japan, that portland cement isalkaline because calcium hydroxide is generated when it comes intocontact with water and, if it is used for ground improvement, the pH ofthe ground increases up to 10, adversely affecting the growth of plants,etc. and that, if portland cement is used for improving ground with lowwater content such as a loamy layer, it becomes easier for hexavalentchromium in the portland cement to elute, adversely affecting theenvironment. Besides the above, there have been proposals for theimprovement of fluidity of cement slurry used for ground improvementsuch as those in Japanese Patent Publications Tokkai 11-256161,2000-169209 and 2006-298726, as well as for hydraulic compositions usingblast-furnace slag, etc. usable also for ground improvement such asthose in Japanese Patent Publications Tokkai 62-158146, 63-2842,1-208354, 10-114555 and 2002-241152, but there have been no detailedreports or proposals contributing to the reduction in emission of carbondioxide.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide slurrycompositions for ground improvement capable of reducing the generationof carbon dioxide by using blast-furnace slag cement at a higher ratethan being done at present such that the workability of groundimprovement work is maintained and the ground would gain necessarystrength, as well as a method of producing soil cement slurry using suchcompositions.

The inventors herein have discovered as a result of their diligentstudies in view of the aforementioned object of the present inventionthat slurry compositions for ground improvement using together with anadmixture a specified kind of blast-furnace slag cement containingblast-furnace slag fine particles at a higher rate and portland cementat a correspondingly lower rate, as well as a method of producing soilcement slurry using such compositions are correctly responsive to theobject of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to slurry compositions for groundimprovement, comprising at least cement, water and an admixture, thecement being blast-furnace slag cement comprising blast-furnace fineparticles with fineness 3000-13000 cm²/g in an amount of 60-80 mass %and portland cement in an amount of 20-40 mass % so as to be together100 mass %, the slurry compositions being produced by mixing water withthis blast-furnace slag cement at a mass ratio of 40-250% and containingthe admixture in an amount of 0.1-5 mass parts per 100 mass parts ofthis blast-furnace slag cement.

The present invention also relates to a method of producing soil cementslurry characterized as using slurry compositions for ground slurryusing blast-furnace slag cement according to this invention at a rate of300-1200 kg per 1 m³ of ground.

A slurry composition for ground improvement using blast-furnace slagcement (hereinafter referred to as a slurry composition of thisinvention) is characterized as comprising at least cement, water and anadmixture. The slurry composition of this invention uses blast-furnaceslag cement of a special kind and such blast-furnace slag cement ischaracterized as containing blast-furnace slag fine particles withfineness 3000-13000 cm²/g in an amount of 60-80 mass % and portlandcement in an amount of 20-40 mass % such that their total would be 100mass % but those containing blast-furnace slag fine particles in anamount of 64-76 mass % and portland cement in an amount of 24-36 mass %such that their total would be 100 mass % are preferable.

Use is made of blast-furnace slag fine particles with fineness in therange of 3000-13000 cm²/g but those with fineness in the range of3000-8000 cm²/g are preferable and those with fineness in the range of3500-6500 cm²/g are more preferable. If those with fineness outside therange of 3000-13000 cm²/g are used, the fluidity of the prepared slurrycomposition may be poor or the resultant ground strength may be lowered.The fineness is herein expressed by the specific surface area by theblain method.

Use as portland cement is usually made of normal portland cement, highearly strength portland cement or moderate heat portland cement, butmulti-purpose normal portland cement is preferable.

For producing a slurry composition of this invention, the mass ratio ofwater to blast-furnace slag cement is adjusted to 40-250%, and morepreferably to 45-230%. If this mass ratio is greater than 250%, thereduction in the ground strength becomes great. If this mass ratio isless than 40%, on the other hand, the fluidity of the soil cement slurrybecomes too low. An admixture is used in a slurry composition of thisinvention in an amount of 0.1-5 mass parts per 100 mass parts of theblast-furnace slag cement. In the above, the mass ratio between waterand blast-furnace cement is the number obtained as ((mass of waterused)/(mass of blast-furnace cement used))×100.

Admixtures that may be used in the slurry compositions of this inventioninclude those used in conventionally known kinds of soil cement.Examples of such admixture include fluidizers, hardening acceleratorsand defoamers.

There is no particular limitation on the fluidizers to be used but thosecomprising alkali metal salts of water soluble vinyl copolymers obtainedby alkali hydrolysis of copolymer between α-olefin and anhydrous maleicacid and having mass averaged molecular weight (throughout herein,pullulan converted weight by gel-permeation chromatography method) of2000-70000 are preferable and those comprising alkali metal salts ofwater soluble vinyl copolymers obtained by alkali hydrolysis ofcopolymer between isobutylene and anhydrous maleic acid are particularpreferable.

Examples of preferable fluidizers further include those comprisingalkali metal salts of polyacrylic acid with mass averaged molecularweight of 1500-50000 and they can be used in combination with theaforementioned alkali metal salt of water soluble vinyl copolymer. Theamount of aforementioned fluidizers to be used is preferably 0.1-4 massparts to 100 mass parts of blast-furnace slag cement, and morepreferably 0.3-3 mass parts.

Examples of hardening accelerator include alkali metal carbonates suchas sodium carbonate, potassium carbonate and lithium carbonate. Amongthese, sodium carbonate is preferable from economic reasons. Thesehardening accelerators are used for improving the strength manifestationcharacteristic of the ground hardener obtained by injecting a slurrycomposition of this invention into ground, drilling and stirring. Theamount of hardening accelerator to be used is preferably 0.3-4 massparts, and more preferably 0.5-3 mass parts, for 100 mass parts ofblast-furnace slag cement.

There is no particular limitation on the defoamer to be used but thoseof polyalkylene glycol monoalkenyl (or alkyl)ether, modifiedpolydimethyl siloxane and trialkyl phosphate can be mentioned. Foreconomic reasons and from the point of view of the degree ofmanifestation of effects, however, defoamers comprising polyalkyleneglycol monoalkenyl ether are preferable. A defoamer is used foreliminating the trouble of foaming when the slurry composition of thisinvention is produced and also for controlling the air to be dragged inwhen the slurry composition is injected into the ground for drilling andstirring to thereby improve the strength manifestation of the groundhardener. The amount of defoamer to be used is preferably 0.001-0.1 massparts, and more preferably 0.002-0.01 mass parts, for 100 mass parts ofblast-furnace slag cement.

Slurry compositions of this invention can be prepared by a known method.For example, they may be prepared by a method of mixing specifiedamounts of blast-furnace slag cement, water and admixture by placingthem into a mixer and kneading them together. At this moment, additivematerials such as bentonite and fibers and additive agents such assetting retarders and hardening accelerators may be added, if necessary,within the limit of not adversely affecting the effects of thisinvention.

In a method of fluidizing the soil cement slurry of this invention, soilcement slurry is produced by mixing a slurry composition of thisinvention described above with ground according to the required fluidityof the soil cement slurry and strength of the ground hardener. At thismoment, the slurry composition of this invention is used in an amount of300-1200 kg, and preferably 400-1100 kg, per 1 m³ of ground.

The present invention has the effect of suppressing the emission ofcarbon dioxide and controlling the lowering in fluidity of prepared soilcement slurry with time by using blast-furnace slag cement of aspecified kind as a cement material together with an admixture in groundimprovement such that superior workability can be maintained and theground hardener can be allowed to manifest necessary strength at thesame time.

In what follows, the invention will be explained in terms of someexamples but these examples are not intended to limit the scope of theinvention. In the following examples, unless otherwise explained, “%”means “mass %”, and “parts” means “mass parts”.

Part 1 Preparation of Fluidizer as Admixture

After water 145 g and 30% caustic soda 470 g were placed in a flaskequipped with a stirrer, copolymer of isobutylene and anhydrous maleicacid (isobam 600 (tradename) produced by Kuraray) 395 g was graduallyadded with stirring while the internal temperature was maintained at 60°C. to obtain alkali metal salt of copolymer by hydrolysis. This wasanalyzed by using GPC (gel-permeation chromatography) method and foundto be sodium salt (p-1) of water soluble vinyl copolymer comprisingsodium salt of copolymer of isobutylene and anhydrous maleic acid andhaving mass averaged molecular weight of 23000. By similar methods,fluidizers (p-2) and (p-3) were prepared.

The fluidizers, hardening accelerators and defoamers used as admixturesin this invention, inclusive of the fluidizers described above, areshown together in Table 1.

TABLE 1 Type Details Fluidizer p-1 Sodium salt of water soluble vinylcopolymer of isobutylene and anhydrous maleic acid with mass averagedmolecular weight = 23000 p-2 Potassium salt of water soluble vinylcopolymer of isobutylene and anhydrous maleic acid with mass averagedmolecular weight = 65000 p-3 Sodium salt of water soluble vinylcopolymer of diisobutylene and anhydrous maleic acid with mass averagedmolecular weight = 34000 p-4 Sodium salt of polyacrylic acid with massaveraged molecular weight = 21000 p-5 Mixture of (p-1) and (p-4) at massratio of 2/1 Hardening c-1 Sodium carbonate accelerator c-2 Potassiumcarbonate Defoamer d-1 Polyalkylene glycol monoalkenyl ether defoamer(AFK-2 (tradename) produced by Takemoto Yushi)

Part 2 Preparation of Blast-Furnace Slag Cement

Blast-furnace slag fine particles and portland cement were used underthe conditions shown in Table 2 to obtain blast-furnace slag cement(S-1)-(S-4) and (R-1)-(R-3).

TABLE 2 Blast-furnace slag cement Mixture of blast-furnace slag fineparticles and portland cement (total of 100 mass parts) Blast-furnaceslag fine particles Portland cement Type Type Ratio (%) Type Ratio (%)S-1 sg-1 70 pc-1 30 S-2 sg-1 75 pc-1 25 S-3 sg-2 65 pc-1 35 S-4 sg-1 70pc-2 30 R-1 sg-1 85 pc-1 15 R-2 sg-1 45 pc-1 55 R-3 sg-3 30 pc-1 70 InTable 2: sg-1: Blast-furnace slag fine particles with fineness 4100cm²/g sg-2: Blast-furnace slag fine particles with fineness 5900 cm²/gsg-3: Blast-furnace slag fine particles with fineness 1020 cm²/g pc-1:Normal portland cement pc-2: High early strength portland cement

Part 3 Preparation of Slurry Compositions for Ground Improvement TestExamples 1-8 and Comparison Examples 1-6

Specified amounts of blast-furnace slag cement shown in Table 2 andkneading water (faucet water) were placed in a forced mixing pan-typemixer under conditions shown in Table 3 and specified amounts offluidizer, hardening accelerator and defoamer shown in Table 1 asadmixtures were also placed inside to be kneaded together to prepareeach example of slurry composition for ground improvement.

TABLE 3 Slurry compositions for ground improvement Ratio of slurrycomposition (total = 100%) Mass ratio Blast- (%) of furnace Admixtureswater/blast- slag cement Water Fluidizer Hardening Deformer furnace(type/used (used (type/used accelerator (type/used slag cement amountamount amount (type/used amount Type (%) (%)) (%)) (%)) amount (%)) (%))TE-1 SL-1 200 S-1/33.3 66.7 p-1/0.4 c-1/2.5 d-1/0.005 TE-2 SL-2 200S-2/33.3 66.7 p-2/0.4 c-1/2.5 d-1/0.005 TE-3 SL-3 200 S-3/33.3 66.7p-3/0.4 c-1/2.5 d-1/0.005 TE-4 SL-4 200 S-1/33.3 66.7 p-4/0.4 c-2/2.5d-1/0.005 TE-5 SL-5 100 S-1/50 50 p-5/1.8 c-1/1.5 d-1/0.003 TE-6 SL-6100 S-3/50 50 p-1/1.8 c-2/1.5 d-1/0.003 TE-7 SL-7 50 S-2/66.7 33.3p-1/2.5 c-1/1.0 d-1/0.002 TE-8 SL-8 50 S-4/66.7 33.3 p-1/2.5 c-2/1.0d-1/0.002 CE-1 RSL-1 200 R-1/33.3 66.7 p-1/0.4 c-1/2.5 d-1/0.005 CE-2RSL-2 200 R-2/33.3 66.7 p-2/0.4 c-1/2.5 d-1/0.005 CE-3 RSL-3 200R-3/33.3 66.7 p-3/0.4 c-1/2.5 d-1/0.005 CE-4 RSL-4 100 S-1/50 50 — — —CE-5 RSL-5 100 R-2/50 50 p-1/1.8 c-2/1.5 d-1/0.003 CE-6 RSL-6 200S-1/33.3 66.7 p-1/0.4 c-1/0.05 d-1/0.005 CE-7 RSL-7 200 S-3/33.3 66.7p-1/0.4 — — CE-8 RSL-8 200 *1/33.3 66.7 p-1/0.4 — — In Table 3: TE: TestExample CE: Comparison Example Type of Blast-furnace slag cement: Asdescribed in Table 2 Types of fluidizers, hardening accelerators anddefoamers: As described in Table 1 Used amounts of fluidizers, hardeningaccelerators and defoamers: Mass parts of solid component per 100 massparts of blast-furnace slag cement *1: Type B blast-furnace slag cement(density = 3.04 g/cm³; blain value = 3850 cm²/g)

Part 4 Preparation and Evaluation of Soil Cement Slurry Test Examples9-16 and Comparison Examples 7-12

Soil cement slurry was prepared by using each example of slurrycompositions for ground improvement prepared in Part 3 and evaluated asfollows. The injected amount of slurry compositions for 1 m³ of groundimprovement was determined such that the target uni-axial compressivestrength at material age of 28 days would be over 5N/mm². A specifiedamount of each slurry composition for ground improvement prepared inPart 3 was firstly placed in a hobart mixer and then ground with thephysical characteristics shown in Table 4 (mixture of cohesive soilobtained by digging ground and silica sand at mass ratio of 3/1) wasadded and mixed together to obtain the samples of soil cement slurryshown in Table 5. Conditions for preparation of each sample are alsoshown in Table 5.

TABLE 4 Mass per Particle density Fraction of particles in volume Watercontent in mixed soil mixed soil (%) (kg/m³) (%) (g/cm₃) Cohesive soilSilica sand 1812 38.6 1.082 66.7 33.3

Evaluation of Physical Characteristics of Prepared Soil Cement Slurry

For each example of soil cement slurry prepared, the flow valueimmediately after the mixing with kneading, the flow value 90 minutesafter the mixing with kneading, the air content and the uni-axialcompressive strength were obtained as follows and the results are showntogether in Table 5. Their emission rates of carbon dioxide are alsoshown.

Flow values: Flow tests were carried out both immediately and 90 minutesafter the mixing with kneading and flow values after elevationdifference (mm) were measured 15 times according to JIS-RS201.

Air content: Obtained according to JIS-A6201 (1977).

Uni-axial compression strength test: Compressive strength (N/mm²) atmaterial age of 28 days was measured on molded articles obtained byusing a mold with diameter 50 mm×height 100 mm according to JIS-A1108.

TABLE 5 Details of soil cement slurry Slurry composition ContentEvaluated physical characteristics for ground of blast- Emmitted Flowvalue improvement Injection furnace amount of (mm) Uni-axial Injectedrate slag carbon 90 Air compressive amount (volume cement dioxide Rightminutes content strength Type (kg) %) (kg) (kg) after later (%) (N/mm²)TE-9 SL-1 1031 80 344 82 226 214 0.6 6.0 TE-10 SL-2 1031 80 344 68 229226 0.5 6.3 TE-11 SL-3 1031 80 344 96 221 207 0.5 6.4 TE-12 SL-4 1031 80344 82 223 212 0.6 6.0 TE-13 SL-5 688 46 344 82 227 214 0.6 9.1 TE-14SL-6 688 46 344 96 224 213 0.6 9.0 TE-15 SL-7 416 29 344 68 231 215 0.513.3 TE-16 SL-8 416 29 344 82 236 218 0.5 12.7 CE-9 RSL-1 1031 80 344 41208 163 0.6 3.2 CE-10 RSL-2 1031 80 344 151 215 142 0.6 2.8 CE-11 RSL-31031 80 344 192 220 121 0.6 5.3 CE-12 RSL-4 1031 46 344 82 136 105 2.84.2 CE-13 RSL-5 1031 46 344 151 225 164 0.9 5.5 CE-14 RSL-6 1031 80 34482 210 153 1.2 4.6 CE-15 RSL-7 1031 80 344 96 202 125 3.2 3.8 CE-16RSL-8 1031 80 344 137 223 162 3.7 4.7 In Table 5: Test ExampleComparison Example Injected amount: Injected amount (kg) of slurrycomposition for ground improvement per 1 m³ Injection rate: Rate ofinjection (volume %) of slurry composition for ground improvement per 1m³ Content of blast-furnace slag cement: Content of blast-furnace slagcement (kg) per 1 m³ Emitted amount of carbon dioxide: Amount of carbondioxide (kg) emitted for improving 1 m³ as calculated from the amount ofportland cement used

As can be understood from Table 5, each example of soil cement slurry ischaracterized by a small amount of carbon dioxide for improving 1 m³ ofground as compared with conventionally used Comparison Example 16 whichemploys Type B blast-furnace slag cement. Moreover, excellent fluidityand fluidity maintaining characteristics with flow values less than 200mm are obtainable, and sufficiently satisfactory results in targetuni-axial compressive strength is attained.

1. A slurry composition for ground improvement, said slurry compositioncomprising cement, water and an admixture, and being prepared by usingwater and blast-furnace slag cement as said cement at awater/blast-furnace slag cement mass ratio of 40-250% and containingsaid admixture in an amount of 0.1-5 mass parts for 100 mass parts ofsaid blast-furnace slag cement, said blast-furnace slag cementcomprising blast-furnace slag fine particles with fineness 3000-13000cm²/g in an amount of 60-80 mass % and portland cement in an amount of20-40 mass % for a total of 100 mass %.
 2. The slurry composition forground improvement of claim 1 wherein said blast-furnace slag fineparticles have fineness 3500-6500 cm²/g.
 3. The slurry composition forground improvement of claim 2 wherein said portland cement is normalportland cement.
 4. The slurry composition for ground improvement ofclaim 2 wherein said blast-furnace slag cement comprises saidblast-furnace slag fine particles in an amount of 64-76 mass % and saidportland cement in an amount of 24-36 mass % for a total of 100 mass %.5. The slurry composition for ground improvement of claim 4 wherein saidadmixture at least partially includes a hardening accelerator comprisingan alkali metal carbonate salt.
 6. The slurry composition for groundimprovement of claim 5 wherein said admixture at least partiallyincludes a defoamer comprising polyalkylene glycol monoalkenyl ether. 7.The slurry composition for ground improvement of claim 6 wherein saidadmixture at least partially includes a fluidizer comprising an alkalimetal salt of water soluble vinyl copolymer obtained by alkalihydrolysis of copolymer of α-olefin and anhydrous maleic acid and havingmass averaged molecular weight of 2000-70000.
 8. The slurry compositionfor ground improvement of claim 6 wherein said admixture at leastpartially includes a fluidizer comprising an alkali metal salt ofpolyacrylic acid having mass averaged molecular weight of 1500-50000. 9.The slurry composition for ground improvement of claim 7 wherein waterand said blast-furnace slag cement are used at a mass ratio of 45-230%.10. The slurry composition for ground improvement of claim 8 whereinwater and said blast-furnace slag cement are used at a mass ratio of45-230%.
 11. A method of preparing soil cement slurry, said methodcomprising the step of using the slurry composition for groundimprovement of claim 9 in an amount of 300-1200 kg per 1 m³ of ground.12. A method of preparing soil cement slurry, said method comprising thestep of using the slurry composition for ground improvement of claim 10in an amount of 300-1200 kg per 1 m³ of ground.